Method for receiving downlink control channel in wireless communication system and device therefor

ABSTRACT

According to one embodiment of the present invention, a method by which a terminal decodes a downlink control channel for a terminal configured so as to support a multi transmission time interval (TTI) length in a wireless communication system can comprise the steps of: receiving information on whether physical resource block (PRB) bundling occurs for a downlink control channel or on bundling size thereof; and decoding downlink control channels at a first TTI on the basis of the assumption that the same precoder has been applied to downlink control channels within the same PRB bundling, when the PRB bundling is configured for the downlink control channel.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is the National Stage filing under 35 U.S.C. 371 ofInternational Application No. PCT/KR2016/013700, filed on Nov. 25, 2016,which claims the benefit of U.S. Provisional Applications No.62/260,245, filed on Nov. 25, 2015, the contents of which are all herebyincorporated by reference herein in their entirety.

TECHNICAL FIELD

The present invention relates to a wireless communication system, andmore particularly, to a method of receiving a downlink control channelin a wireless communication system and an apparatus therefor.

BACKGROUND ART

In a wireless cellular communication system, discussion on a method ofperforming transmission and reception capable of reducing latency asmuch as possible by transmitting data as soon as possible during a shorttime period using a short TTI (transmission time interval) for aservice/UE sensitive to latency and transmitting a response within shorttime in response to the data is in progress. On the contrary, it maytransmit and receive data using a longer TTI for a service/UE lesssensitive to the latency. For a service/UE sensitive to power efficiencyrather than the latency, it may repetitively transmit data with the samelower power or transmit data using a lengthened TTI. The presentinvention proposes a method of receiving downlink control informationthat enables the abovementioned operation.

DISCLOSURE OF THE INVENTION Technical Task

A technical task of the present invention is to provide a method ofreceiving a downlink control channel in a wireless communication systemand an operation related to the method.

Technical tasks obtainable from the present invention are non-limitedthe above-mentioned technical task. And, other unmentioned technicaltasks can be clearly understood from the following description by thosehaving ordinary skill in the technical field to which the presentinvention pertains.

Technical Solution

To achieve these and other advantages and in accordance with the purposeof the present invention, as embodied and broadly described, accordingto one embodiment, a method of decoding a downlink control channel for aterminal configured to support multiple TTI (transmission time interval)lengths in a wireless communication system, which is performed by theterminal and includes receiving information on whether or not PRB(physical resource block) bundle is configured on the downlink controlchannel or information on a size of the PRB bundle, and when the PRBbundle is configured for the downlink control channel, decoding downlinkcontrol channels in a first TTI under the assumption that the sameprecoder is applied to downlink control channels within the same PRBbundle.

Additionally or alternatively, the downlink control channels may beassigned to continuous PRBs or discontinuous PRBs.

Additionally or alternatively, the size of the PRB bundle may be definedto be identical or different to/from a PRG (precoding resource group)size.

Additionally or alternatively, when a terminal-specific reference signalis not received in the first TTI, the method may further include using aterminal-specific reference signal received in a different TTI.

Additionally or alternatively, the method may further include receivinginformation on a configuration of a TTI window in which aterminal-specific reference signal usable in the first TTI istransmitted.

Additionally or alternatively, the method may further include decodingthe downlink control channels in the first TTI by utilizing at least apart of terminal-specific reference signals received within the TTIwindow indicated by the received information on the configuration of theTTI window.

Additionally or alternatively, the number of resource element groups,which construct a control channel element for the downlink controlchannel received in the first TTI, may be determined according to alength of a TTI.

Additionally or alternatively, an aggregation level of a control channelelement for the downlink control channel received in the first TTI maybe adjusted according to a length of a TTI.

Additionally or alternatively, the method may further include receivinginformation on a frequency resource region to be used for a set of thedownlink control channels which are determined according to a length ofa TTI.

To further achieve these and other advantages and in accordance with thepurpose of the present invention, according to a different embodiment, aterminal configured to support multiple TTI (transmission time interval)lengths in a wireless communication system includes a transmitter and areceiver, and a processor that controls the transmitter and thereceiver, the processor controls the receiver to receive information onwhether or not PRB (physical resource block) bundle is configured on thedownlink control channel or information on a size of the PRB bundle, andwhen the PRB bundling is configured for the downlink control channel,decodes downlink control channels in a first TTI under the assumptionthat the same precoder is applied to downlink control channels withinthe same PRB bundle.

Additionally or alternatively, the downlink control channels may beassigned to continuous PRBs or discontinuous PRBs.

Additionally or alternatively, the size of the PRB bundle may be definedto be identical or different to/from a PRG (precoding resource group)size.

Additionally or alternatively, if a terminal-specific reference signalis not received in the first TTI, the processor may use aterminal-specific reference signal received in a different TTI.

Additionally or alternatively, the processor may control the receiver toreceive information on a configuration of a TTI window in which aterminal-specific reference signal usable in the first TTI istransmitted.

Additionally or alternatively, the processor may decodes the downlinkcontrol channels in the first TTI by utilizing at least a part ofterminal-specific reference signals received within the TTI windowindicated by the received information on the configuration of the TTIwindow.

Additionally or alternatively, the number of resource element groups,which construct a control channel element for the downlink controlchannel received in the first TTI, may be determined according to alength of a TTI.

Additionally or alternatively, an aggregation level of a control channelelement for the downlink control channel received in the first TTI maybe adjusted according to a length of a TTI.

Additionally or alternatively, the processor may controls the receiverto receive information on a frequency resource region to be used for aset of the downlink control channels which are determined according to alength of a TTI.

Technical solutions obtainable from the present invention arenon-limited the above-mentioned technical solutions. And, otherunmentioned technical solutions can be clearly understood from thefollowing description by those having ordinary skill in the technicalfield to which the present invention pertains.

Advantageous Effects

According to one embodiment of the present invention, it is able toefficiently transmit or receive a downlink control channel in a wirelesscommunication system.

Effects obtainable from the present invention may be non-limited by theabove mentioned effect. And, other unmentioned effects can be clearlyunderstood from the following description by those having ordinary skillin the technical field to which the present invention pertains.

DESCRIPTION OF DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention and are incorporated in and constitute apart of this specification, illustrate embodiments of the invention andtogether with the description serve to explain the principles of theinvention.

FIG. 1 is a diagram for an example of a radio frame structure used in awireless communication system;

FIG. 2 is a diagram for an example of a downlink (DL)/uplink (UL) slotstructure in a wireless communication system;

FIG. 3 is a diagram for an example of a downlink (DL) subframe structureused in 3GPP LTE/LTE-A system;

FIG. 4 is a diagram for an example of an uplink (UL) subframe structureused in 3GPP LTE/LTE-A system;

FIG. 5 is a diagram illustrating DL reception timing and UL transmissiontiming of UEs operating with a different TTI (transmission timeinterval);

FIG. 6 illustrates EREG-to-RE mapping method according to one embodimentof the present invention;

FIG. 7 illustrates EREG-to-RE mapping method according to one embodimentof the present invention;

FIG. 8 illustrates a method of configuring ECCE according to oneembodiment of the present invention;

FIG. 9 is a flowchart for an operation according to one embodiment ofthe present invention;

FIG. 10 is a block diagram of a device for implementing embodiment(s) ofthe present invention.

BEST MODE

Mode for Invention

Reference will now be made in detail to the preferred embodiments of thepresent invention, examples of which are illustrated in the accompanyingdrawings. The accompanying drawings illustrate exemplary embodiments ofthe present invention and provide a more detailed description of thepresent invention. However, the scope of the present invention shouldnot be limited thereto.

In some cases, to prevent the concept of the present invention frombeing ambiguous, structures and apparatuses of the known art will beomitted, or will be shown in the form of a block diagram based on mainfunctions of each structure and apparatus. Also, wherever possible, thesame reference numbers will be used throughout the drawings and thespecification to refer to the same or like parts.

In the present invention, a user equipment (UE) is fixed or mobile. TheUE is a device that transmits and receives user data and/or controlinformation by communicating with a base station (BS). The term ‘UE’ maybe replaced with ‘terminal equipment’, ‘Mobile Station (MS)’, ‘MobileTerminal (MT)’, ‘User Terminal (UT)’, ‘Subscriber Station (SS)’,‘wireless device’, ‘Personal Digital Assistant (PDA)’, ‘wireless modem’,‘handheld device’, etc. A BS is typically a fixed station thatcommunicates with a UE and/or another BS. The BS exchanges data andcontrol information with a UE and another BS. The term BS' may bereplaced with ‘Advanced Base Station (ABS)’, ‘Node B’, ‘evolved-Node B(eNB)’, ‘Base Transceiver System (BTS)’, ‘Access Point (AP)’,‘Processing Server (PS)’, etc. In the following description, BS iscommonly called eNB.

In the present invention, a node refers to a fixed point capable oftransmitting/receiving a radio signal to/from a UE by communication withthe UE. Various eNBs can be used as nodes. For example, a node can be aBS, NB, eNB, pico-cell eNB (PeNB), home eNB (HeNB), relay, repeater,etc. Furthermore, a node may not be an eNB. For example, a node can be aradio remote head (RRH) or a radio remote unit (RRU). The RRH and RRUhave power levels lower than that of the eNB. Since the RRH or RRU(referred to as RRH/RRU hereinafter) is connected to an eNB through adedicated line such as an optical cable in general, cooperativecommunication according to RRH/RRU and eNB can be smoothly performedcompared to cooperative communication according to eNBs connectedthrough a wireless link. At least one antenna is installed per node. Anantenna may refer to an antenna port, a virtual antenna or an antennagroup. A node may also be called a point. Unlike a conventionalcentralized antenna system (CAS) (i.e. single node system) in whichantennas are concentrated in an eNB and controlled an eNB controller,plural nodes are spaced apart at a predetermined distance or longer in amulti-node system. The plural nodes can be managed by one or more eNBsor eNB controllers that control operations of the nodes or schedule datato be transmitted/received through the nodes. Each node may be connectedto an eNB or eNB controller managing the corresponding node via a cableor a dedicated line. In the multi-node system, the same cell identity(ID) or different cell IDs may be used for signal transmission/receptionthrough plural nodes. When plural nodes have the same cell ID, each ofthe plural nodes operates as an antenna group of a cell. If nodes havedifferent cell IDs in the multi-node system, the multi-node system canbe regarded as a multi-cell (e.g., macro-cell/femto-cell/pico-cell)system. When multiple cells respectively configured by plural nodes areoverlaid according to coverage, a network configured by multiple cellsis called a multi-tier network. The cell ID of the RRH/RRU may beidentical to or different from the cell ID of an eNB. When the RRH/RRUand eNB use different cell IDs, both the RRH/RRU and eNB operate asindependent eNBs.

In a multi-node system according to the present invention, which will bedescribed below, one or more eNBs or eNB controllers connected to pluralnodes can control the plural nodes such that signals are simultaneouslytransmitted to or received from a UE through some or all nodes. Whilethere is a difference between multi-node systems according to the natureof each node and implementation form of each node, multi-node systemsare discriminated from single node systems (e.g. CAS, conventional MIMOsystems, conventional relay systems, conventional repeater systems,etc.) since a plurality of nodes provides communication services to a UEin a predetermined time-frequency resource. Accordingly, embodiments ofthe present invention with respect to a method of performing coordinateddata transmission using some or all nodes can be applied to varioustypes of multi-node systems. For example, a node refers to an antennagroup spaced apart from another node by a predetermined distance ormore, in general. However, embodiments of the present invention, whichwill be described below, can even be applied to a case in which a noderefers to an arbitrary antenna group irrespective of node interval. Inthe case of an eNB including an X-pole (cross polarized) antenna, forexample, the embodiments of the preset invention are applicable on theassumption that the eNB controls a node composed of an H-pole antennaand a V-pole antenna.

A communication scheme through which signals are transmitted/receivedvia plural transmit (Tx)/receive (Rx) nodes, signals aretransmitted/received via at least one node selected from plural Tx/Rxnodes, or a node transmitting a downlink signal is discriminated from anode transmitting an uplink signal is called multi-eNB MIMO or CoMP(Coordinated Multi-Point Tx/Rx). Coordinated transmission schemes fromamong CoMP communication schemes can be categorized into JP (JointProcessing) and scheduling coordination. The former may be divided intoJT (Joint Transmission)/JR (Joint Reception) and DPS (Dynamic PointSelection) and the latter may be divided into CS (CoordinatedScheduling) and CB (Coordinated Beamforming). DPS may be called DCS(Dynamic Cell Selection). When JP is performed, more variouscommunication environments can be generated, compared to other CoMPschemes. JT refers to a communication scheme by which plural nodestransmit the same stream to a UE and JR refers to a communication schemeby which plural nodes receive the same stream from the UE. The UE/eNBcombine signals received from the plural nodes to restore the stream. Inthe case of JT/JR, signal transmission reliability can be improvedaccording to transmit diversity since the same stream is transmittedfrom/to plural nodes. DPS refers to a communication scheme by which asignal is transmitted/received through a node selected from plural nodesaccording to a specific rule. In the case of DPS, signal transmissionreliability can be improved because a node having a good channel statebetween the node and a UE is selected as a communication node.

In the present invention, a cell refers to a specific geographical areain which one or more nodes provide communication services. Accordingly,communication with a specific cell may mean communication with an eNB ora node providing communication services to the specific cell. Adownlink/uplink signal of a specific cell refers to a downlink/uplinksignal from/to an eNB or a node providing communication services to thespecific cell. A cell providing uplink/downlink communication servicesto a UE is called a serving cell. Furthermore, channel status/quality ofa specific cell refers to channel status/quality of a channel or acommunication link generated between an eNB or a node providingcommunication services to the specific cell and a UE. In 3GPP LTE-Asystems, a UE can measure downlink channel state from a specific nodeusing one or more CSI-RSs (Channel State Information Reference Signals)transmitted through antenna port(s) of the specific node on a CSI-RSresource allocated to the specific node. In general, neighboring nodestransmit CSI-RS resources on orthogonal CSI-RS resources. When CSI-RSresources are orthogonal, this means that the CSI-RS resources havedifferent subframe configurations and/or CSI-RS sequences which specifysubframes to which CSI-RSs are allocated according to CSI-RS resourceconfigurations, subframe offsets and transmission periods, etc. whichspecify symbols and subcarriers carrying the CSI RSs.

In the present invention, PDCCH (Physical Downlink ControlChannel)/PCFICH (Physical Control Format Indicator Channel)/PHICH(Physical Hybrid automatic repeat request Indicator Channel)/PDSCH(Physical Downlink Shared Channel) refer to a set of time-frequencyresources or resource elements respectively carrying DCI (DownlinkControl Information)/CFI (Control Format Indicator)/downlink ACK/NACK(Acknowledgement/Negative ACK)/downlink data. In addition, PUCCH(Physical Uplink Control Channel)/PUSCH (Physical Uplink SharedChannel)/PRACH (Physical Random Access Channel) refer to sets oftime-frequency resources or resource elements respectively carrying UCI(Uplink Control Information)/uplink data/random access signals. In thepresent invention, a time-frequency resource or a resource element (RE),which is allocated to or belongs toPDCCH/PCFICH/PHICH/PDSCH/PUCCH/PUSCH/PRACH, is referred to as aPDCCH/PCFICH/PHICH/PDSCH/PUCCH/PUSCH/PRACH RE orPDCCH/PCFICH/PHICH/PDSCH/PUCCH/PUSCH/PRACH resource. In the followingdescription, transmission of PUCCH/PUSCH/PRACH by a UE is equivalent totransmission of uplink control information/uplink data/random accesssignal through or on PUCCH/PUSCH/PRACH. Furthermore, transmission ofPDCCH/PCFICH/PHICH/PDSCH by an eNB is equivalent to transmission ofdownlink data/control information through or onPDCCH/PCFICH/PHICH/PDSCH.

FIG. 1 illustrates an exemplary radio frame structure used in a wirelesscommunication system. FIG. 1(a) illustrates a frame structure forfrequency division duplex (FDD) used in 3GPP LTE/LTE-A and FIG. 1(b)illustrates a frame structure for time division duplex (TDD) used in3GPP LTE/LTE-A.

Referring to FIG. 1, a radio frame used in 3GPP LTE/LTE-A has a lengthof 10 ms (307200 Ts) and includes 10 subframes in equal size. The 10subframes in the radio frame may be numbered. Here, Ts denotes samplingtime and is represented as Ts=1/(2048*15 kHz). Each subframe has alength of 1 ms and includes two slots. 20 slots in the radio frame canbe sequentially numbered from 0 to 19. Each slot has a length of 0.5 ms.A time for transmitting a subframe is defined as a transmission timeinterval (TTI). Time resources can be discriminated by a radio framenumber (or radio frame index), subframe number (or subframe index) and aslot number (or slot index).

The radio frame can be configured differently according to duplex mode.Downlink transmission is discriminated from uplink transmission byfrequency in FDD mode, and thus the radio frame includes only one of adownlink subframe and an uplink subframe in a specific frequency band.In TDD mode, downlink transmission is discriminated from uplinktransmission by time, and thus the radio frame includes both a downlinksubframe and an uplink subframe in a specific frequency band.

Table 1 shows DL-UL configurations of subframes in a radio frame in theTDD mode.

TABLE 1 Downlink- DL-UL to-Uplink configu- Switch-point Subframe numberration periodicity 0 1 2 3 4 5 6 7 8 9 0 5 ms D S U U U D S U U U 1 5 msD S U U D D S U U D 2 5 ms D S U D D D S U D D 3 10 ms D S U U U D D D DD 4 10 ms D S U U D D D D D D 5 10 ms D S U D D D D D D D 6 5 ms D S U UU D S U U D

In Table 1, D denotes a downlink subframe, U denotes an uplink subframeand S denotes a special subframe. The special subframe includes threefields of DwPTS (Downlink Pilot TimeSlot), GP (Guard Period), and UpPTS(Uplink Pilot TimeSlot). DwPTS is a period reserved for downlinktransmission and UpPTS is a period reserved for uplink transmission.Table 2 shows special subframe configuration.

TABLE 2 Normal cyclic prefix in downlink Extended cyclic prefix indownlink UpPTS UpPTS Special Normal Extended Normal Extended subframecyclic prefix cyclic prefix cyclic prefix cyclic prefix configurationDwPTS in uplink in uplink DwPTS in uplink in uplink 0  6592 · T_(s) 2192· T_(s) 2560 · T_(s)  7680 · T_(s) 2192 · T_(s) 2560 · T_(s) 1 19760 ·T_(s) 20480 · T_(s) 2 21952 · T_(s) 23040 · T_(s) 3 24144 · T_(s) 25600· T_(s) 4 26336 · T_(s)  7680 · T_(s) 4384 · T_(s) 5120 · T_(s) 5  6592· T_(s) 4384 · T_(s) 5120 · T_(s) 20480 · T_(s) 6 19760 · T_(s) 23040 ·T_(s) 7 21952 · T_(s) 12800 · T_(s) 8 24144 · T_(s) — — — 9 13168 ·T_(s) — — —

FIG. 2 illustrates an exemplary downlink/uplink slot structure in awireless communication system. Particularly, FIG. 2 illustrates aresource grid structure in 3GPP LTE/LTE-A. A resource grid is presentper antenna port.

Referring to FIG. 2, a slot includes a plurality of OFDM (OrthogonalFrequency Division Multiplexing) symbols in the time domain and aplurality of resource blocks (RBs) in the frequency domain. An OFDMsymbol may refer to a symbol period. A signal transmitted in each slotmay be represented by a resource grid composed of N_(RB) ^(DL/UL)*N_(sc)^(RB) subcarriers and N_(symb) ^(DL/UL) OFDM symbols. Here, N_(RB) ^(DL)denotes the number of RBs in a downlink slot and N_(RB) ^(UL) denotesthe number of RBs in an uplink slot. N_(RB) ^(DL) and N_(RB) ^(DL)respectively depend on a DL transmission bandwidth and a UL transmissionbandwidth. N_(symb) ^(DL) denotes the number of OFDM symbols in thedownlink slot and N_(symb) ^(UL) denotes the number of OFDM symbols inthe uplink slot. In addition, NB_(sc) ^(RB) denotes the number ofsubcarriers constructing one RB.

An OFDM symbol may be called an SC-FDM (Single Carrier FrequencyDivision Multiplexing) symbol according to multiple access scheme. Thenumber of OFDM symbols included in a slot may depend on a channelbandwidth and the length of a cyclic prefix (CP). For example, a slotincludes 7 OFDM symbols in the case of normal CP and 6 OFDM symbols inthe case of extended CP. While FIG. 2 illustrates a subframe in which aslot includes 7 OFDM symbols for convenience, embodiments of the presentinvention can be equally applied to subframes having different numbersof OFDM symbols. Referring to FIG. 2, each OFDM symbol includes N_(RB)^(DL/UL)*N_(sc) ^(RB) subcarriers in the frequency domain. Subcarriertypes can be classified into a data subcarrier for data transmission, areference signal subcarrier for reference signal transmission, and nullsubcarriers for a guard band and a direct current (DC) component. Thenull subcarrier for a DC component is a subcarrier remaining unused andis mapped to a carrier frequency (f0) during OFDM signal generation orfrequency up-conversion. The carrier frequency is also called a centerfrequency.

An RB is defined by N_(symb) ^(DL/UL) (e.g., 7) consecutive OFDM symbolsin the time domain and N_(sc) ^(RB) (e.g., 12) consecutive subcarriersin the frequency domain. For reference, a resource composed by an OFDMsymbol and a subcarrier is called a resource element (RE) or a tone.Accordingly, an RB is composed of N_(symb) ^(DL/UL)*N_(sc) ^(RB) REs.Each RE in a resource grid can be uniquely defined by an index pair (k,l) in a slot. Here, k is an index in the range of 0 to N_(symb)^(DL/UL)*N_(sc) ^(RB)−1 in the frequency domain and l is an index in therange of 0 to N_(symb) ^(DL/UL)−1.

Two RBs that occupy N_(sc) ^(RB) consecutive subcarriers in a subframeand respectively disposed in two slots of the subframe are called aphysical resource block (PRB) pair. Two RBs constituting a PRB pair havethe same PRB number (or PRB index). A virtual resource block (VRB) is alogical resource allocation unit for resource allocation. The VRB hasthe same size as that of the PRB. The VRB may be divided into alocalized VRB and a distributed VRB depending on a mapping scheme of VRBinto PRB. The localized VRBs are mapped into the PRBs, whereby VRBnumber (VRB index) corresponds to PRB number. That is, nPRB=nVRB isobtained. Numbers are given to the localized VRBs from 0 to N_(VRB)^(DL)−1, and N_(VRB) ^(DL)=N_(RB) ^(DL) is obtained. Accordingly,according to the localized mapping scheme, the VRBs having the same VRBnumber are mapped into the PRBs having the same PRB number at the firstslot and the second slot. On the other hand, the distributed VRBs aremapped into the PRBs through interleaving. Accordingly, the VRBs havingthe same VRB number may be mapped into the PRBs having different PRBnumbers at the first slot and the second slot. Two PRBs, which arerespectively located at two slots of the subframe and have the same VRBnumber, will be referred to as a pair of VRBs.

FIG. 3 illustrates a downlink (DL) subframe structure used in 3GPPLTE/LTE-A.

Referring to FIG. 3, a DL subframe is divided into a control region anda data region. A maximum of three (four) OFDM symbols located in a frontportion of a first slot within a subframe correspond to the controlregion to which a control channel is allocated. A resource regionavailable for PDCCH transmission in the DL subframe is referred to as aPDCCH region hereinafter. The remaining OFDM symbols correspond to thedata region to which a physical downlink shared chancel (PDSCH) isallocated. A resource region available for PDSCH transmission in the DLsubframe is referred to as a PDSCH region hereinafter. Examples ofdownlink control channels used in 3GPP LTE include a physical controlformat indicator channel (PCFICH), a physical downlink control channel(PDCCH), a physical hybrid ARQ indicator channel (PHICH), etc. ThePCFICH is transmitted at a first OFDM symbol of a subframe and carriesinformation regarding the number of OFDM symbols used for transmissionof control channels within the subframe. The PHICH is a response ofuplink transmission and carries an HARQ acknowledgment (ACK)/negativeacknowledgment (NACK) signal.

Control information carried on the PDCCH is called downlink controlinformation (DCI). The DCI contains resource allocation information andcontrol information for a UE or a UE group. For example, the DCIincludes a transport format and resource allocation information of adownlink shared channel (DL-SCH), a transport format and resourceallocation information of an uplink shared channel (UL-SCH), paginginformation of a paging channel (PCH), system information on the DL-SCH,information about resource allocation of an upper layer control messagesuch as a random access response transmitted on the PDSCH, a transmitcontrol command set with respect to individual UEs in a UE group, atransmit power control command, information on activation of a voiceover IP (VoIP), downlink assignment index (DAI), etc. The transportformat and resource allocation information of the DL-SCH are also calledDL scheduling information or a DL grant and the transport format andresource allocation information of the UL-SCH are also called ULscheduling information or a UL grant. The size and purpose of DCIcarried on a PDCCH depend on DCI format and the size thereof may bevaried according to coding rate. Various formats, for example, formats 0and 4 for uplink and formats 1, 1A, 1B, 1C, 1D, 2, 2A, 2B, 2C, 3 and 3Afor downlink, have been defined in 3GPP LTE. Control information such asa hopping flag, information on RB allocation, modulation coding scheme(MCS), redundancy version (RV), new data indicator (NDI), information ontransmit power control (TPC), cyclic shift demodulation reference signal(DMRS), UL index, channel quality information (CQI) request, DLassignment index, HARQ process number, transmitted precoding matrixindicator (TPMI), precoding matrix indicator (PMI), etc. is selected andcombined based on DCI format and transmitted to a UE as DCI.

In general, a DCI format for a UE depends on transmission mode (TM) setfor the UE. In other words, only a DCI format corresponding to aspecific TM can be used for a UE configured in the specific TM.

A PDCCH is transmitted on an aggregation of one or several consecutivecontrol channel elements (CCEs). The CCE is a logical allocation unitused to provide the PDCCH with a coding rate based on a state of a radiochannel. The CCE corresponds to a plurality of resource element groups(REGs). For example, a CCE corresponds to 9 REGs and an REG correspondsto 4 REs. 3GPP LTE defines a CCE set in which a PDCCH can be located foreach UE. A CCE set from which a UE can detect a PDCCH thereof is calleda PDCCH search space, simply, search space. An individual resourcethrough which the PDCCH can be transmitted within the search space iscalled a PDCCH candidate. A set of PDCCH candidates to be monitored bythe UE is defined as the search space. In 3GPP LTE/LTE-A, search spacesfor DCI formats may have different sizes and include a dedicated searchspace and a common search space. The dedicated search space is aUE-specific search space and is configured for each UE. The commonsearch space is configured for a plurality of UEs. Aggregation levelsdefining the search space is as follows.

TABLE 3 Search Space Aggregation Number of PDCCH Type Level L Size [inCCEs] candidates M^((L)) UE-specific 1 6 6 2 12 6 4 8 2 8 16 2 Common 416 4 8 16 2

A PDCCH candidate corresponds to 1, 2, 4 or 8 CCEs according to CCEaggregation level. An eNB transmits a PDCCH (DCI) on an arbitrary PDCCHcandidate with in a search space and a UE monitors the search space todetect the PDCCH (DCI). Here, monitoring refers to attempting to decodeeach PDCCH in the corresponding search space according to all monitoredDCI formats. The UE can detect the PDCCH thereof by monitoring pluralPDCCHs. Since the UE does not know the position in which the PDCCHthereof is transmitted, the UE attempts to decode all PDCCHs of thecorresponding DCI format for each subframe until a PDCCH having the IDthereof is detected. This process is called blind detection (or blinddecoding (BD)).

The eNB can transmit data for a UE or a UE group through the dataregion. Data transmitted through the data region may be called userdata. For transmission of the user data, a physical downlink sharedchannel (PDSCH) may be allocated to the data region. A paging channel(PCH) and downlink-shared channel (DL-SCH) are transmitted through thePDSCH. The UE can read data transmitted through the PDSCH by decodingcontrol information transmitted through a PDCCH. Informationrepresenting a UE or a UE group to which data on the PDSCH istransmitted, how the UE or UE group receives and decodes the PDSCH data,etc. is included in the PDCCH and transmitted. For example, if aspecific PDCCH is CRC (cyclic redundancy check)-masked having radionetwork temporary identify (RNTI) of “A” and information about datatransmitted using a radio resource (e.g., frequency position) of “B” andtransmission format information (e.g., transport block size, modulationscheme, coding information, etc.) of “C” is transmitted through aspecific DL subframe, the UE monitors PDCCHs using RNTI information anda UE having the RNTI of “A” detects a PDCCH and receives a PDSCHindicated by “B” and “C” using information about the PDCCH.

A reference signal (RS) to be compared with a data signal is necessaryfor the UE to demodulate a signal received from the eNB. A referencesignal refers to a predetermined signal having a specific waveform,which is transmitted from the eNB to the UE or from the UE to the eNBand known to both the eNB and UE. The reference signal is also called apilot. Reference signals are categorized into a cell-specific RS sharedby all UEs in a cell and a modulation RS (DM RS) dedicated for aspecific UE. A DM RS transmitted by the eNB for demodulation of downlinkdata for a specific UE is called a UE-specific RS. Both or one of DM RSand CRS may be transmitted on downlink. When only the DM RS istransmitted without CRS, an RS for channel measurement needs to beadditionally provided because the DM RS transmitted using the sameprecoder as used for data can be used for demodulation only. Forexample, in 3GPP LTE(-A), CSI-RS corresponding to an additional RS formeasurement is transmitted to the UE such that the UE can measurechannel state information. CSI-RS is transmitted in each transmissionperiod corresponding to a plurality of subframes based on the fact thatchannel state variation with time is not large, unlike CRS transmittedper subframe.

FIG. 4 illustrates an exemplary uplink subframe structure used in 3GPPLTE/LTE-A.

Referring to FIG. 4, a UL subframe can be divided into a control regionand a data region in the frequency domain. One or more PUCCHs (physicaluplink control channels) can be allocated to the control region to carryuplink control information (UCI). One or more PUSCHs (Physical uplinkshared channels) may be allocated to the data region of the UL subframeto carry user data.

In the UL subframe, subcarriers spaced apart from a DC subcarrier areused as the control region. In other words, subcarriers corresponding toboth ends of a UL transmission bandwidth are assigned to UCItransmission. The DC subcarrier is a component remaining unused forsignal transmission and is mapped to the carrier frequency f0 duringfrequency up-conversion. A PUCCH for a UE is allocated to an RB pairbelonging to resources operating at a carrier frequency and RBsbelonging to the RB pair occupy different subcarriers in two slots.Assignment of the PUCCH in this manner is represented as frequencyhopping of an RB pair allocated to the PUCCH at a slot boundary. Whenfrequency hopping is not applied, the RB pair occupies the samesubcarrier.

The PUCCH can be used to transmit the following control information.

-   -   Scheduling Request (SR): This is information used to request a        UL-SCH resource and is transmitted using On-Off Keying (OOK)        scheme.    -   HARQ ACK/NACK: This is a response signal to a downlink data        packet on a PDSCH and indicates whether the downlink data packet        has been successfully received. A 1-bit ACK/NACK signal is        transmitted as a response to a single downlink codeword and a        2-bit ACK/NACK signal is transmitted as a response to two        downlink codewords. HARQ-ACK responses include positive ACK        (ACK), negative ACK (NACK), discontinuous transmission (DTX) and        NACK/DTX. Here, the term HARQ-ACK is used interchangeably with        the term HARQ ACK/NACK and ACK/NACK.    -   Channel State Indicator (CSI): This is feedback information        about a downlink channel. Feedback information regarding MIMO        includes a rank indicator (RI) and a precoding matrix indicator        (PMI).

The quantity of control information (UCI) that a UE can transmit througha subframe depends on the number of SC-FDMA symbols available forcontrol information transmission. The SC-FDMA symbols available forcontrol information transmission correspond to SC-FDMA symbols otherthan SC-FDMA symbols of the subframe, which are used for referencesignal transmission. In the case of a subframe in which a soundingreference signal (SRS) is configured, the last SC-FDMA symbol of thesubframe is excluded from the SC-FDMA symbols available for controlinformation transmission. A reference signal is used to detect coherenceof the PUCCH. The PUCCH supports various formats according toinformation transmitted thereon.

Table 4 shows the mapping relationship between PUCCH formats and UCI inLTE/LTE-A.

TABLE 4 Number of bits per PUCCH Modulation subframe, format schemeM_(bit) Usage Etc. 1 N/A N/A SR (Scheduling Request) 1a BPSK 1 ACK/NACKor One SR + ACK/NACK codeword 1b QPSK 2 ACK/NACK or Two SR + ACK/NACKcodeword 2 QPSK 20 CQI/PMI/RI Joint coding ACK/NACK (extended CP) 2aQPSK + 21 CQI/PMI/RI + Normal CP BPSK ACK/NACK only 2b QPSK + 22CQI/PMI/RI + Normal CP QPSK ACK/NACK only 3 QPSK 48 ACK/NACK or SR +ACK/NACK or CQI/PMI/RI + ACK/NACK

Referring to Table 4, PUCCH formats 1/1a/1b are used to transmitACK/NACK information, PUCCH format 2/2a/2b are used to carry CSI such asCQI/PMI/RI and PUCCH format 3 is used to transmit ACK/NACK information.

CSI Reporting

In the 3GPP LTE(-A) system, a user equipment (UE) is defined to reportCSI to a BS. Herein, the CSI collectively refers to informationindicating the quality of a radio channel (also called a link) createdbetween a UE and an antenna port. The CSI includes, for example, a rankindicator (RI), a precoding matrix indicator (PMI), and a channelquality indicator (CQI). Herein, the RI, which indicates rankinformation about a channel, refers to the number of streams that a UEreceives through the same time-frequency resource. The RI value isdetermined depending on long-term fading of the channel, and is thususually fed back to the BS by the UE with a longer period than for thePMI and CQI. The PMI, which has a value reflecting the channel spaceproperty, indicates a precoding index preferred by the UE based on ametric such as SINR. The CQI, which has a value indicating the intensityof a channel, typically refers to a receive SINR which may be obtainedby the BS when the PMI is used.

The UE calculates, based on measurement of the radio channel, apreferred PMI and RI from which an optimum or highest transmission ratemay be derived when used by the BS in the current channel state, andfeeds back the calculated PMI and RI to the BS. Herein, the CQI refersto a modulation and coding scheme providing an acceptable packet errorprobability for the PMI/RI that is fed back.

In the LTE-A system which is expected to include more precise MU-MIMOand explicit CoMP operations, current CSI feedback is defined in LTE,and thus new operations to be introduced may not be sufficientlysupported. As requirements for CSI feedback accuracy for obtainingsufficient MU-MIMO or CoMP throughput gain became complicated, it hasbeen agreed that the PMI should be configured with a long term/widebandPMI (W₁) and a short term/subband PMI (W₂). In other words, the finalPMI is expressed as a function of W₁ and W₂. For example, the final PMIW may be defined as follows: W=W₁*W₂ or W=W₂*W₁. Accordingly, in LTE-A,the CSI may include RI, W₁, W₂ and CQI.

In the 3GPP LTE(-A) system, an uplink channel used for CSI transmissionis configured as shown in Table 5.

TABLE 5 Scheduling scheme Periodic CSI transmission Aperiodic CSItransmission Frequency non-selective PUCCH — Frequency selective PUCCHPUSCH

Referring to Table 5, CSI may be transmitted with a periodicity definedin a higher layer, using a physical uplink control channel (PUCCH). Whenneeded by the scheduler, a physical uplink shared channel (PUSCH) may beaperiodically used to transmit the CSI. Transmission of the CSI over thePUSCH is possible only in the case of frequency selective scheduling andaperiodic CSI transmission. Hereinafter, CSI transmission schemesaccording to scheduling schemes and periodicity will be described.

1) Transmitting the CQI/PMI/RI Over the PUSCH after Receiving a CSITransmission Request Control Signal (a CSI Request)

A PUSCH scheduling control signal (UL grant) transmitted over a PDCCHmay include a control signal for requesting transmission of CSI. Thetable below shows modes of the UE in which the CQI, PMI and RI aretransmitted over the PUSCH.

TABLE 6 PMI Feedback Type No PMI Single PMI Multiple PMIs PUSCH CQIWideband Mode 1-2 Feedback Type (Wideband CQI) RI 1st wideband CQI(4bit) 2nd wideband CQI(4 bit) if RI >1 N * Subband PMI(4 bit) (N is thetotal # of subbands) (if 8Tx Ant, N * subband W2 + wideband W1) UEselected Mode 2-0 Mode 2-2 (Subband CQI) RI (only for Open- RI loop SM)1st wideband 1st wideband CQI(4 bit) + Best-M CQI(4 bit) + Best-M CQI(2bit) CQI(2 bit) 2nd wideband (Best-M CQI: An CQI(4 bit) + Best-M averageCQI for M CQI(2 bit) if RI >1 SBs selected from Best-M index (L among NSBs) bit) Best-M index (L Wideband bit) PMI(4 bit) + Best-M PMI(4 bit)(if 8Tx Ant, wideband W2 + Best-M W2 + wideband W1) Higher Layer- Mode3-0 Mode 3-1 Mode 3-2 configured RI (only for Open- RI RI (Subband CQI)loop SM) 1st wideband 1st wideband 1st wideband CQI(4 bit) + CQI(4bit) + CQI(4 bit) + N * subband N * subbandCQI(2 bit) N * subbandCQI(2bit) CQI(2 bit) 2nd wideband 2nd wideband CQI(4 bit) + CQI(4 bit) + N *subbandCQI(2 bit) N * subbandCQI(2 bit) if RI >1 if RI >1 Wideband N *Subband PMI(4 bit) PMI(4 bit) (if 8Tx Ant, (N is the total # of widebandW2 + subbands) wideband W1) (if 8Tx Ant, N * subband W2 + wideband W1)

The transmission modes in Table 6 are selected in a higher layer, andthe CQI/PMI/RI are all transmitted in a PUSCH subframe. Hereinafter,uplink transmission methods for the UE according to the respective modeswill be described.

Mode 1-2 represents a case where precoding matrices are selected on theassumption that data is transmitted only in subbands. The UE generates aCQI on the assumption of a precoding matrix selected for a system bandor a whole band (set S) designated in a higher layer. In Mode 1-2, theUE may transmit a CQI and a PMI value for each subband. Herein, the sizeof each subband may depend on the size of the system band.

A UE in Mode 2-0 may select M preferred subbands for a system band or aband (set S) designated in a higher layer. The UE may generate one CQIvalue on the assumption that data is transmitted for the M selectedsubbands. Preferably, the UE additionally reports one CQI (wideband CQI)value for the system band or set S. If there are multiple codewords forthe M selected subbands, the UE defines a CQI value for each codeword ina differential form.

In this case, the differential CQI value is determined as a differencebetween an index corresponding to the CQI value for the M selectedsubbands and a wideband (WB) CQI index.

The UE in Mode 2-0 may transmit, to a BS, information about thepositions of the M selected subbands, one CQI value for the M selectedsubbands and a CQI value generated for the whole band or designated band(set S). Herein, the size of a subband and the value of M may depend onthe size of the system band.

A UE in Mode 2-2 may select positions of M preferred subbands and asingle precoding matrix for the M preferred subbands simultaneously onthe assumption that data is transmitted through the M preferredsubbands. Herein, a CQI value for the M preferred subbands is definedfor each codeword. In addition, the UE additionally generates a widebandCQI value for the system band or a designated band (set S).

The UE in Mode 2-2 may transmit, to the BS, information about thepositions of the M preferred subbands, one CQI value for the M selectedsubbands and a single PMI for the M preferred subbands, a wideband PMI,and a wideband CQI value. Herein, the size of a subband and the value ofM may depend on the size of the system band.

A UE in Mode 3-0 generates a wideband CQI value. The UE generates a CQIvalue for each subband on the assumption that data is transmittedthrough each subband. In this case, even if RI>1, the CQI valuerepresents only the CQI value for the first codeword.

A UE in Mode 3-1 generates a single precoding matrix for the system bandor a designated band (set S). The UE generates a CQI subband for eachcodeword on the assumption of the single precoding matrix generated foreach subband. In addition, the UE may generate a wideband CQI on theassumption of the single precoding matrix. The CQI value for eachsubband may be expressed in a differential form. The subband CQI valueis calculated as a difference between the subband CQI index and thewideband CQI index. Herein, the size of each subband may depend on thesize of the system band.

A UE in Mode 3-2 generates a precoding matrix for each subband in placeof a single precoding matrix for the whole band, in contrast with the UEin Mode 3-1.

2) Periodic CQI/PMI/RI transmission over PUCCH

The UE may periodically transmit CSI (e.g., CQI/PMI/PTI (precoding typeindicator) and/or RI information) to the BS over a PUCCH. If the UEreceives a control signal instructing transmission of user data, the UEmay transmit a CQI over the PUCCH. Even if the control signal istransmitted over a PUSCH, the CQI/PMI/PTI/RI may be transmitted in oneof the modes defined in the following table.

TABLE 7 PMI feedback type No PMI Single PMI PUCCH CQI Wideband Mode 1-0Mode 1-1 feedback type (wideband CQI) UE selective Mode 2-0 Mode 2-1(subband CQI)

A UE may be set in transmission modes as shown in Table 7. Referring toTable 7, in Mode 2-0 and Mode 2-1, a bandwidth part (BP) may be a set ofsubbands consecutively positioned in the frequency domain, and cover thesystem band or a designated band (set S). In Table 9, the size of eachsubband, the size of a BP and the number of BPs may depend on the sizeof the system band. In addition, the UE transmits CQIs for respectiveBPs in ascending order in the frequency domain so as to cover the systemband or designated band (set S).

The UE may have the following PUCCH transmission types according to atransmission combination of CQI/PMI/PTI/RI.

i) Type 1: the UE transmits a subband (SB) CQI of Mode 2-0 and Mode 2-1.

ii) Type 1a: the UE transmits an SB CQI and a second PMI.

iii) Types 2, 2b and 2c: the UE transmits a WB-CQI/PMI.

iv) Type 2a: the UE transmits a WB PMI.

v) Type 3: the UE transmits an RI.

vi) Type 4: the UE transmits a WB CQI.

vii) Type 5: the UE transmits an RI and a WB PMI.

viii) Type 6: the UE transmits an RI and a PTI.

When the UE transmits an RI and a WB CQI/PMI, the CQI/PMI aretransmitted in subframes having different periodicities and offsets. Ifthe RI needs to be transmitted in the same subframe as the WB CQI/PMI,the CQI/PMI are not transmitted.

Aperiodic CSI Request

Currently, the LTE standard uses the 2-bit CSI request field in DCIformat 0 or 4 to operate aperiodic CSI feedback when considering acarrier aggregation (CA) environment. When the UE is configured withseveral serving cells in the CA environment, the CSI request field isinterpreted as two bits. If one of the TMs 1 through 9 is set for allCCs (Component Carriers), aperiodic CSI feedback is triggered accordingto the values in Table 8 below, and TM 10 for at least one of the CCs Ifset, aperiodic CSI feedback is triggered according to the values inTable 9 below.

TABLE 8 A value of CSI request field Description ‘00’ No aperiodic CSIreport is triggered ‘01’ Aperiodic CSI report is triggered for a servingcell ‘10’ Aperiodic CSI report is triggered for a first group of servingcells configured by a higher layer ‘11’ Aperiodic CSI report istriggered for a second group of serving cells configured by a higherlayer

TABLE 9 A value of CSI request field Description ‘00’ No aperiodic CSIreport is triggered ‘01’ Aperiodic CSI report is triggered for a CSIprocess group configured by a higher layer for a serving cell ‘10’Aperiodic CSI report is triggered for a first group of CSI processesconfigured by a higher layer ‘11’ Aperiodic CSI report is triggered fora second group of CSI processes configured by a higher layer

The present invention relates to a method of providing a plurality ofdifferent services in a system by applying a different service parameteraccording to a service or a UE to satisfy a requirement of each of aplurality of the services. In particular, the present invention relatesto a method of reducing latency as much as possible by transmitting dataas soon as possible during a short time period using a short TTI(transmission time interval) for a service/UE sensitive to latency andtransmitting a response within short time in response to the data. Onthe contrary, it may transmit and receive data using a longer TTI for aservice/UE less sensitive to the latency. For a service/UE sensitive topower efficiency rather than the latency, it may repetitively transmitdata with the same lower power or transmit data using a lengthened TTI.The present invention proposes a method of transmitting controlinformation and a data signal for enabling the abovementioned operationand a multiplexing method.

For clarity, 1 ms currently used in LTE/LTE-A system is assumed as abasic TTI. A basic system is also based on LTE/LTE-A system. When adifferent service/UE is provided in a base station of LTE/LTE-A systembased on a TTI of 1 ms (i.e., a subframe length), a method oftransmitting a data/control channel having a TTI unit shorter than 1 msis proposed for a service/UE sensitive to latency. In the following, aTTI of 1 ms is referred to as a normal TTI, a TTI of a unit smaller than1 ms (e.g., 0.5 ms) is referred to as a short TTI, and a TTI of a unitlonger than 1 ms (e.g., 2 ms) is referred to as a long TTI.

First of all, a method of supporting a short TTI of a unit shorter than1 ms in a system basically using a normal TTI of 1 ms unit used inlegacy LTE/LTE-A system is described. First of all, downlink (DL) isexplained. Multiplexing between channels having a different TTI size inan eNB and an example of uplink (UL) transmission for the multiplexingare shown in FIG. 5. As a TTI is getting shorter, time taken for a UE tobuffer and decode a control channel and a data channel is gettingshorter. Time taken for performing UL transmission in response to thecontrol channel and the data channel is getting shorter. As shown in theexample of FIG. 5, in case of transmission of 1 ms TTI, when a DLchannel is transmitted in a specific n^(th) subframe, an eNB can receivea response in an (n+4)^(th) subframe in response to the DL channel. Incase of transmission of 0.5 TTI, when a DL channel is transmitted in aspecific n^(th) subframe, an eNB can receive a response in an (n+2)^(th)subframe in response to the DL channel. In particular, in order tosupport TTIs of a different length, it is necessary to support backwardcompatibility to prevent an impact on a UE operating in a legacy systemonly for DL and UL multiplexing of channels having a different TTI.

When DL/UL channels having a different length of TTI are multiplexed, itis necessary to define a method for a UE, which has received thechannels, to read a control channel and transmit/receive a data channel.A UE supporting a normal TTI only, a UE supporting a normal TTI and ashort TTI, and a UE supporting a normal TTI, a short TTI, and a long TTImay coexist in a system. In this case, when a UE supports a short TTIand a normal TTI, it means that the UE is able to receive and demodulateboth a channel transmitted with a short TTI (“short TTI channel”) and achannel transmitted with a normal TTI (“normal TTI channel”) and is ableto generate and transmit the short TTI channel and the normal TTIchannel in UL.

In a legacy LTE/LTE-A system, one subframe, i.e., a TTI, has a length of1 ms and one subframe includes two slots. One slot corresponds to 0.5ms. In case of a normal CP, one slot includes 7 OFDM symbols. A PDCCH(physical downlink control channel) is positioned at a forepart of asubframe and is transmitted over the whole band. A PDSCH (physicaldownlink shared channel) is transmitted after the PDCCH. PDSCHs of UEsare multiplexed on a frequency axis after a PDCCH section. In order fora UE to receive PDSCH of the UE, the UE should know a position to whichthe PDSCH is transmitted. Information on the position, MCS information,RS information, antenna information, information on a transmissionscheme, information on a transmission mode (TM), and the like can beobtained via the PDCCH. For clarity, PDCCH having a short TTI and PDSCHhaving a short TTI are referred to as sPDCCH and sPDSCH, respectively.If a UE receives the sPDSCH, the UE transmits HARQ-ACK via a PUCCH(physical uplink control channel) in response to the sPDSCH. In thiscase, a PUCCH having a short TTI is referred to as sPUCCH.

EPDCCH Resource Mapping

If a short TTI is introduced, unlike a legacy rule, it may be able todefine a rule that EPDCCH is to be transmitted via a partial OFDM symbolonly within a subframe. Specifically, When EPDCCH is transmitted with ashort TTI, it may define an EREG-to-RE mapping rule different from alegacy mapping rule. FIG. 6 illustrates an example of EPDCCH resourcemapping when a short TTI is introduced.

It is able to perform EREG-to-RE mapping according to a frequency-firsttime-second rule within a short TTI. For example, as shown in FIG. 6, ifa TTI of 0.5 ms is assumed, 5 REs are mapped to EREGs 0 to 7. On thecontrary, 4 REs are mapped to EREGs 8 to 15. For reference, in FIG. 6, anumber in an RE (rectangular) corresponds to a number of an EREG group(i.e., 0 to 16). Yet, the number of REs constructing a single ECCE isthe same.

As a different method, it may perform EREG-to-RE mapping on theremaining part except a legacy PDCCH region. In other word, it may beable to perform EREG-to-RE mapping from an OFDM symbol corresponding toEPDCCH start point within a short TTI. It is illustrated in FIG. 7.

If a short TTI is introduced, an amount of resources to be transmittedor an amount of resources for transmitting EPDCCH can be reducedcompared to a legacy EPDCCH having the same aggregation level. Hence,the number of EREGs constructing a single ECCE can be defined in advanceby a number greater than 4 or 8 according to a TTI length.

According to current LTE standard (refer to the following), 16 EREGsexist in a single PRB pair.

[Reference 1]

There are 16 EREGs, numbered from 0 to 15, per physical resource blockpair. Number all resource elements, except resource elements carryingDM-RS for antenna ports p={107, 108, 109, 110} for normal cyclic prefixor p={107, 108} for extended cyclic prefix, in a physical resource-blockpair cyclically from 0 to 15 in an increasing order of first frequency,then time. All resource elements with number i in that physicalresource-block pair constitutes EREG number i.

(There are 16 EREGs, numbered from 0 to 15, per physical resource blockpair. Number all resource elements, except resource elements carryingDM-RS for antenna ports p={107, 108, 109, 110} for normal cyclic prefixor p={107, 108} for extended cyclic prefix, in a physical resource-blockpair cyclically from 0 to 15 in an increasing order of first frequency,then time. All resource elements with number i in that physicalresource-block pair constitutes EREG number i.)

If a short TTI is introduced, the number of EREGs existing in a TTI canbe defined by 24 in advance. In this case, although the short TTI isintroduced, it may be able to make the number of EREGs constructing eachECCE to be relatively similar. Or, it may be able to define that oneECCE is to be configured by 6 EREGs. In this case, an example ofEREG-to-RE mapping is shown in FIG. 8.

If a short TTI is introduced, an amount of resources to be transmittedor an amount of resources for transmitting EPDCCH can be reducedcompared to a legacy EPDCCH having the same aggregation level. Hence, itmay be able to define a rule that an aggregation level is to becontrolled according to a length of a TTI. It may be able to define arule that a separate EPDCCH set is to be configured for a short TTI.

And, a frequency resource region to be used for a specific EPDCCH setcan be separately indicated according to a TTI length. According to arelated art, 2, 4, or 8 PRB pairs were used for a specific EPDCCH set.

EPDCCH Reception

According to current LTE standard, channel estimation is performed usinga UE-specific RS (e.g., DMRS) existing in each PRB pair in which EPDCCHis transmitted to decode the EPDCCH. A reference 2 in the followingcorresponds to the contents for the current standard.

[Reference 2]

UE-specific reference signals associated with PDSCH are transmitted onantenna port(s) p=5, p=7, p=8, or one or several of p ϵ {7, 8, 9, 10,11, 12, 13, 14}. The channel over which a symbol on one of these antennaports is conveyed can be inferred from the channel over which anothersymbol on the same antenna port is conveyed only if the two symbols arewithin the same subframe and in the same PRG (precoding resource group)when PRB bundling is used or in the same PRB pair when PRB bundling isnot used.

Demodulation reference signals associated with EPDCCH are transmitted onone or several of p ϵ {107, 108, 109, 110}. The channel over which asymbol on one of these antenna ports is conveyed can be inferred fromthe channel over which another symbol on the same antenna port isconveyed only if the two symbols are in the same PRB pair.

(UE-specific reference signals associated with PDSCH are transmitted onantenna port(s) p=5, p=7, p=8, or one or several of p ϵ {7, 8, 9, 10,11, 12, 13, 14}. The channel over which a symbol on one of these antennaports is conveyed can be inferred from the channel over which anothersymbol on the same antenna port is conveyed only if the two symbols arewithin the same subframe and in the same PRG (precoding resource group)when PRB bundling is used or in the same PRB pair when PRB bundling isnot used.

Demodulation reference signals associated with EPDCCH are transmitted onone or several of p ϵ {107, 108, 109, 110}. The channel over which asymbol on one of these antenna ports is conveyed can be inferred fromthe channel over which another symbol on the same antenna port isconveyed only if the two symbols are in the same PRB pair.)

If a short TTI is introduced, it is necessary to perform channelestimation using the relatively less number of symbols compared to alegacy TTI. Hence, it is anticipated that accuracy of the channelestimation is to be degraded. In order to solve the problem, the presentinvention proposes methods described in the following.

-   -   If a PRB allocated for EPDCCH is within a bundling size which is        determined according to a DL BW, a UE may assume that the same        precoder is applied. The UE can utilize the same precoder for        estimating a channel and decoding EPDCCH. For example, in case        of a system of which a BW corresponds to 50 RBs, if a bundling        size corresponds to 3 RBs and PRB indexes allocated for        transmitting EPDCCH correspond to 0, 1, 2, 3, and 4, a UE may        assume that the same precoder is applied in PRB indexes 0, 1,        and 2 and the UE may also assume that the same precoder is        applied in PRB indexes 3 and 4.    -   And, although PRB indexes are discontinuously allocated, it may        be able to assume that the same precoder is applied within a        bundling size. For example, when PRB indexes 0, 2, and 4 are        allocated, it may assume that the same precoder is applied        within the PRB indexes 0 and 2.    -   An eNB can inform a UE of whether or not PRB bundling is        performed on EPDCCH via higher layer signaling. Or, the eNB can        inform the UE of whether or not PRB bundling is performed on        EPDCCH via physical layer signaling. And, for a bundling size        for the EPDCCH, it may identically reuse a legacy PRG (precoding        resource group) size. Or, it may be able to separately define or        signal the bundling size for the EPDCCH.

When a short TTI is introduced, a UE-specific RS may not exist in aspecific TTI. When EPDCCH is transmitted during the specific TTI,following methods are proposed to perform channel estimation anddecoding on the EPDCCH.

-   -   In order to decode EPDCCH, a UE may use a UE-specific RS of a        different TTI rather than a TTI during which the EPDCCH is        transmitted and the UE can perform EPDCCH decoding via the        UE-specific RS. (Time-domain bundling for EPDCCH).    -   In order to support the abovementioned operation of the UE, a        time window capable of being used for estimating/decoding a        channel can be defined in advance (according to a system        bandwidth) or an eNB can signal the time window to the UE. For        example, when a time window for estimating/decoding a channel of        a specific TTI is configured by the M number of TTIs, if a        UE-specific RS does not exist in an OFDM symbol period        corresponding to a TTI #n, a UE may assume that the same        precoder is applied to a UE-specific RS within the M number of        TTIs including the TTI #n and the UE can perform EPDCCH decoding        by using all or a part of the M number of TTIs.

FIG. 9 is a flowchart for an operation according to one embodiment ofthe present invention.

FIG. 9 illustrates a method of receiving a downlink control channel fora UE configured to support multiple TTI (transmission time interval)lengths in a wireless communication system.

The UE can receive information on whether or not PRB (physical resourceblock) bundling is performed on a downlink control channel orinformation on a bundling size [S910]. If PRB bundling is configured forthe downlink control channel, the UE can decode downlink controlchannels in a first TTI under the assumption that the same precoder isapplied to the downlink control channels within the same PRB bundling[S920].

And, the downlink control channels can be assigned to continuous PRBs ordiscontinuous PRBs. And, the bundling size can be defined by a sizeidentical or different to/from a PRG (precoding resource group) size.

If a UE-specific reference signal is not received during the first TTI,the UE may use a UE-specific reference signal, which is received duringa different TTI, to perform decoding on the downlink control channel.

And, the UE can receive information on a TTI window configuration forwhich a UE-specific reference signal usable in the first TTI istransmitted.

And, the UE can perform decoding on the downlink control channels in thefirst TTI by utilizing at least a part of UE-specific reference signalswhich are received within the TTI window indicated by the information onthe TTI window configuration. The number of resource element groups,which construct a control channel element for the downlink controlchannels received in the first TTI, can be determined according to a TTIlength. An aggregation level of the control channel element for thedownlink control channels received in the first TTI can be adjustedaccording to a length of a TTI.

And, the UE can receive information on a frequency resource region to beused for a set of the downlink control channels which are determinedaccording to a length of a TTI.

In the foregoing description, embodiments of the present invention havebeen briefly explained with reference to FIG. 9. An embodiment relatedto FIG. 9 can alternatively or additionally include at least a part ofthe aforementioned embodiments.

Since it is able to include the examples for the proposed method as oneof implementation methods of the present invention, it is apparent thatthe examples are considered as a sort of proposed methods. Although theembodiments of the present invention can be independently implemented,the embodiments can also be implemented in a combined/aggregated form ofa part of embodiments. It may define a rule that an eNB/location serverinforms a UE of information on whether to apply the proposed methods(or, information on rules of the proposed methods) via a predefinedsignal (e.g., physical layer signal or higher layer signal).

FIG. 10 is a block diagram illustrating a transmitting device 10 and areceiving device 20 configured to implement embodiments of the presentinvention. Each of the transmitting device 10 and receiving device 20includes a transmitter/receiver 13, 23 capable of transmitting orreceiving a radio signal that carries information and/or data, a signal,a message, etc., a memory 12, 22 configured to store various kinds ofinformation related to communication with a wireless communicationsystem, and a processor 11, 21 operatively connected to elements such asthe transmitter/receiver 13, 23 and the memory 12, 22 to control thememory 12, 22 and/or the transmitter/receiver 13, 23 to allow the deviceto implement at least one of the embodiments of the present inventiondescribed above.

The memory 12, 22 may store a program for processing and controlling theprocessor 11, 21, and temporarily store input/output information. Thememory 12, 22 may also be utilized as a buffer. The processor 11, 21controls overall operations of various modules in the transmittingdevice or the receiving device. Particularly, the processor 11, 21 mayperform various control functions for implementation of the presentinvention. The processors 11 and 21 may be referred to as controllers,microcontrollers, microprocessors, microcomputers, or the like. Theprocessors 11 and 21 may be achieved by hardware, firmware, software, ora combination thereof. In a hardware configuration for an embodiment ofthe present invention, the processor 11, 21 may be provided withapplication specific integrated circuits (ASICs) or digital signalprocessors (DSPs), digital signal processing devices (DSPDs),programmable logic devices (PLDs), and field programmable gate arrays(FPGAs) that are configured to implement the present invention. In thecase which the present invention is implemented using firmware orsoftware, the firmware or software may be provided with a module, aprocedure, a function, or the like which performs the functions oroperations of the present invention. The firmware or software configuredto implement the present invention may be provided in the processor 11,21 or stored in the memory 12, 22 to be driven by the processor 11, 21.

The processor 11 of the transmitter 10 performs predetermined coding andmodulation of a signal and/or data scheduled by the processor 11 or ascheduler connected to the processor 11, and then transmits a signaland/or data to the transmitter/receiver 13. For example, the processor11 converts a data sequence to be transmitted into K layers throughdemultiplexing and channel coding, scrambling, and modulation. The codeddata sequence is referred to as a codeword, and is equivalent to atransport block which is a data block provided by the MAC layer. Onetransport block is coded as one codeword, and each codeword istransmitted to the receiving device in the form of one or more layers.To perform frequency-up transformation, the transmitter/receiver 13 mayinclude an oscillator. The transmitter/receiver 13 may include Nttransmit antennas (wherein Nt is a positive integer greater than orequal to 1).

The signal processing procedure in the receiving device 20 is configuredas a reverse procedure of the signal processing procedure in thetransmitting device 10. The transmitter/receiver 23 of the receivingdevice 20 receives a radio signal transmitted from the transmitingdevice 10 under control of the processor 21. The transmitter/receiver 23may include Nr receive antennas, and retrieves baseband signals byfrequency down-converting the signals received through the receiveantennas. The transmitter/receiver 23 may include an oscillator toperform frequency down-converting. The processor 21 may perform decodingand demodulation on the radio signal received through the receiveantennas, thereby retrieving data that the transmitting device 10 hasoriginally intended to transmit.

The transmitter/receiver 13, 23 includes one or more antennas. Accordingto an embodiment of the present invention, the antennas function totransmit signals processed by the transmitter/receiver 13, 23 are toreceive radio signals and deliver the same to the transmitter/receiver13, 23. The antennas are also called antenna ports. Each antenna maycorrespond to one physical antenna or be configured by a combination oftwo or more physical antenna elements. A signal transmitted through eachantenna cannot be decomposed by the receiving device 20 anymore. Areference signal (RS) transmitted in accordance with a correspondingantenna defines an antenna from the perspective of the receiving device20, enables the receiving device 20 to perform channel estimation on theantenna irrespective of whether the channel is a single radio channelfrom one physical antenna or a composite channel from a plurality ofphysical antenna elements including the antenna. That is, an antenna isdefined such that a channel for delivering a symbol on the antenna isderived from a channel for delivering another symbol on the sameantenna. An transmitter/receiver supporting the Multiple-InputMultiple-Output (MIMO) for transmitting and receiving data using aplurality of antennas may be connected to two or more antennas.

In embodiments of the present invention, the UE or the terminal operatesas the transmitting device 10 on uplink, and operates as the receivingdevice 20 on downlink. In embodiments of the present invention, the eNBor the base station operates as the receiving device 20 on uplink, andoperates as the transmitting device 10 on downlink.

The transmitting device and/or receiving device may be implemented byone or more embodiments of the present invention among the embodimentsdescribed above.

Detailed descriptions of preferred embodiments of the present inventionhave been given to allow those skilled in the art to implement andpractice the present invention. Although descriptions have been given ofthe preferred embodiments of the present invention, it will be apparentto those skilled in the art that various modifications and variationscan be made in the present invention defined in the appended claims.Thus, the present invention is not intended to be limited to theembodiments described herein, but is intended to have the widest scopeconsistent with the principles and novel features disclosed herein.

INDUSTRIAL APPLICABILITY

The present invention is applicable to wireless communication devicessuch as a terminal, a relay, and a base station.

What is claimed is:
 1. A method of decoding a downlink control channelfor a terminal in a wireless communication system, comprising:receiving, by the terminal, information on a frequency resource regionto be used for a set for the downlink control channel in which thedownlink control channel is decoded which are determined according to alength of a transmission time interval (TTI) in which the downlinkcontrol channel is decoded; receiving, by the terminal, informationabout a size of a bundle for the downlink control channel; and when thebundle is configured for the downlink control channel, decoding, by theterminal, the downlink control channel in the frequency resource regionunder the assumption that a same precoder is applied to the downlinkcontrol channel within the size of the bundle.
 2. The method of claim 1,wherein the size of the bundle corresponds multiple PRBs (physicalresource blocks).
 3. The method of claim 1, wherein the downlink controlchannel is assigned to continuous PRBs (physical resource blocks) ordiscontinuous PRBs.
 4. The method of claim 1, wherein the size of thePRB is defined to be identical to or different from a PRG (precodingresource group) size.
 5. The method of claim 1, further comprising: whena terminal-specific reference signal is not received during the TTI inwhich the downlink control channel is decoded, using a terminal-specificreference signal received in a different TTI.
 6. The method of claim 5,further comprising receiving information on a configuration of a TTIwindow in which a terminal-specific reference signal usable in the TTIin which the downlink control channel is decoded is transmitted.
 7. Themethod of claim 6, further comprising decoding the downlink controlchannel in the TTI by utilizing at least a part of a terminal-specificreference signal received within the TTI window indicated by thereceived information on the configuration of the TTI window.
 8. Themethod of claim 1, wherein a number of resource element groups, whichconstruct a control channel element for the downlink control channelreceived in the TTI in which the downlink control channel is decoded, isdetermined according to the length of the TTI.
 9. The method of claim 1,wherein an aggregation level of a control channel element for thedownlink control channel received in the TTI in which the downlinkcontrol channel is decoded is adjusted according to the length of theTTI.
 10. A terminal in a wireless communication system, comprising: atransmitter and a receiver; and a processor that controls thetransmitter and the receiver, the processor controls the receiver toreceive information on a frequency resource region to be used for a setfor the downlink control channel in which the downlink control channelis decoded which are determined according to a length of transmissiontime interval (TTI) in which the downlink control channel is decoded,and to receive information about a size of a bundle for the downlinkcontrol channel, and when the bundle is configured for the downlinkcontrol channel, decodes the downlink control channel in the frequencyresource region under the assumption that a same precoder is applied todownlink control channel within the size of the bundle.
 11. The terminalof claim 10, wherein the size of the bundle corresponds multiple PRBs(physical resource blocks).
 12. The terminal of claim 10, wherein thedownlink control channel is assigned to continuous PRBs (physicalresource blocks) or discontinuous PRBs.
 13. The terminal of claim 10,wherein the size of the PRB is defined to be identical to or differentfrom a PRG (precoding resource group) size.
 14. The terminal of claim10, wherein when a terminal-specific reference signal is not receivedduring the TTI in which the downlink control channel is decoded, theprocessor uses a terminal-specific reference signal received in adifferent TTI.
 15. The terminal of claim 14, wherein the processorcontrols the receiver to receive information on a configuration of a TTIwindow in which a terminal-specific reference signal usable in the TTIin which the downlink control channel is decoded is transmitted.
 16. Theterminal of claim 15, wherein the processor decodes the downlink controlchannel in the TTI by utilizing at least a part of a terminal-specificreference signal received within the TTI window indicated by thereceived information on the configuration of the TTI window.
 17. Theterminal of claim 10, wherein a number of resource element groups, whichconstruct a control channel element for the downlink control channelreceived in the TTI in which the downlink control channel is decoded, isdetermined according to the length of the TTI.
 18. The terminal of claim10, wherein an aggregation level of a control channel element for thedownlink control channel received in the TTI in which the downlinkcontrol channel is decoded is adjusted according to the length of theTTI.